1. Technical Field of the Invention
Compliance with the standard IEC 555-2 (IEC 1000-3-2) by AC/DC converters requires the latter to reduce the injection of harmonics into the AC mains supply which otherwise impair its quality. Consequently there exists a concern among designers of AC/DC converters to improve the power factor correction of the converter in order to suppress the harmonics which these devices inject into the AC mains supply.
The AC/DC power converter device of the invention corrects the power factor and is of special, but not exclusive, application in communications systems in which high efficiency converters are required which are light in weight, small in size and inexpensive.
2. Description of Related Art
To satisfy the content of the standards currently in force, AC/DC converters with power factor correction are based on power flow analysis.
This technique for AC/DC converter design is known, for example, from the article "A NOVEL SINGLE-PHASE POWER FACTOR CORRECTION SCHEME", by Yimin Jiang, Fred C. Lee, Guichao Hua and Wei Tang, Proceedings of the Eighth Annual Applied Power Electronics Conference (APEC'93), Mar. 7-11, 1993, San Diego, California, U.S.A., pages 287 to 292.
In this article it is shown that, in parallel with the path followed by the main power flow, there is another power flow that is transferred to the load through what is termed the power factor correction circuit, in such a manner that the correcting circuit does not process all the power that is transferred to the load.
Consequently, there is a part of the input power, representing about the 68% of the average input power, that is transferred directly to the converter output and which is therefore only processed once; the rest of the input power, representing about the 32% of the input power, is processed twice by the power factor correction circuit.
In other words, the power factor correction circuit only transfers power to the output when the input power is less than the average value of the output power, assuming the input power to be a sine squared function. Likewise, when the input power is greater than the output power, the excess energy is stored in the power factor correction circuit, specifically in its capacitor.
Thus the main power flow is transferred directly to the load through a full-wave bridge booster converter and the power factor correction circuit, which transfers the stored power to the load, is formed by a capacitor and a forward converter.
The problem with this technique lies in the control of the switching elements in the full-wave bridge booster converter, since it must distinguish between the periods when the power level is greater than or less than the average value of the output power. Consequently the switching control signals for the switching elements take different values in each cycle.
So, the objective is to achieve an AC/DC converter designed around a simple topology, with few components and simple switching control, and which provides a high power factor and a high efficiency.